Shale gas and other unconventional energies universally adopt long distance horizontal drilling technology to raise drilling efficiency. As oil-based drilling fluid has strong inhibitive ability and outstanding lubricity and is conducive to borehole stability, it is widely applied in the drilling process of extended reach wells and horizontal wells.
Oil-based drilling fluid is a drilling fluid system using oil as a continuous phase and brine as a dispersion phase and formed by adding emulsifier, organic clay and oleophilic colloid. In oil-based drilling fluid, because organic clay can hardly form a strong matrix structure as bentonite does in water-based drilling fluid, the suspension stability is usually poor, leading to difficulty in carrying rock cuttings out of borehole in extended reach sections and horizontal sections.
At present, in China, organic clay and oleophylic colloid are mainly used as tackifier and shear strength-improving agent of oil-based drilling fluid to raise the yield point of drilling fluid, but as the shear strength-improving effect is poor, a large amount of organic clay and/or oleophylic colloid need to be added. As a result, oil-based drilling fluid system is more likely to suffer from thickening problems after aging or circulating at high temperature as well as worsening of theological properties. The above problems are more prominent in high-density oil-based drilling fluid, including diesel-based and mineral oil-based drilling fluid.